This invention relates to a process for aftertreating dyed and/or printed textiles to remove excess portions of colorants utilizing an aqueous formulation comprising at least one graft copolymer having a hydrophilic main chain and also surfactants.
Fibers composed of polyester are widely used raw materials for producing textile materials. Textiles composed of polyester fibers can be dyed in from aqueous baths by means of various dyeing processes and/or printed by means of suitable textile printing colors. For instance, polyesters can be exhaust dyed with disperse dyes at 120°-130° C.
After textiles have been dyed they are typically afterwashed to remove any excess colorant from their surface, since unfixed dyes can lead to marking off of the textiles (unwanted transfer of color to another material). Moreover, unfixed dyes can cause discoloration of differently colored textiles in a washing or laundering operation.
The excess dye left on the surface can be removed for example by means of a reduction clear with hydrosulfite and NaOH at 60-70° C. Thereafter, the textile material is typically rinsed, from 1 to 3 times depending on the depth of shade. The last rinse bath is preferably used to set the pH of the textile material to 4-7 with acetic acid.
It is further known to reduction clear using hydroxymethanesulfinic acid or derivatives thereof. The disadvantage of this method is that it is not suitable for all dyes, particularly not for some hydroquinone derivatives.
A third known method comprises using surfactants for after-washing. But surfactants alone generally do not have a sufficient effect.
Further details of such after wash operations are represented for example in Textile Dyeing, in particular Chapter 7 Dyeing of Polyester Fibers and also Textile Auxiliaries, in particular capital 5.10 Aftertreatment Agents to Improve Fastness, each in Ullmann's Encyclopedia of Industrial Chemistry, Online Edition 2008, Wiley-VCH, Weinheim, N.Y. 2005.
Polypropylene is a polymer that is outstandingly useful for producing textile materials, but textiles composed of polypropylene fibers are very difficult to dye from aqueous baths because of the apolar character of polypropylene. It is therefore known to improve the post-extrusion dyeability of polypropylene from aqueous dyebaths by addition of suitable auxiliaries.
WO 2006/098730, for example, discloses a disperse-dyeable fiber comprising a mixture of a polyolefin with an amorphous, glycol-modified PET (PET-G). Maleic anhydride is preferably used as an additional auxiliary.
WO 2006/128796 discloses a process for dyeing polyolefins which comprises utilizing polyolefins blended with a block copolymer comprising at least one apolar block constructed essentially of isobutene units and also at least one polar block constructed essentially of oxyalkylene units. Polyesters and/or polyamides may be incorporated as auxiliaries in addition to the block copolymer.
Such textiles composed of doped polypropylene can be dyed similarly to polyesters.
However, with textiles composed of doped polypropylene there is a risk that the colored doped polypropylene can be at least partially decolorized by a strong reduction clear. Even a very weak reduction clear (2 g/l of hydrosulfite and 0.5 g/L of NaOH) is observed to result in a loss of depth of shade for the dyed textile.